Indicating plug fuse



March 13, 1934. F. c. LA MAR 1,951,309

INDICATING PLUG FUSE Original Filed Sept. 15, 1932 INVENTOR- 5, m z ATTORNEY Patented Mar. 13, 1934 UNITED STATES PATENT OFFICE.

Application September 15, 1932, Serial No. 633,285 Renewed January 24, 1934 8 Claims. (Cl. 200121) This invention relates to electrical devices, particularly to the thermal fuses for use in connection with electrical circuits, and more especially to what is known as a plug fuse, combined with means for indicating the integrity of the fusible element.

It is quite universally known that it is necessary to protect electrical circuits by means of devices, such as thermal fuses, which melt or be-= come disintegrated or destroyed when an excessive flow of current passes through the circuit of which the fuse forms a part. An especially well known form of thermal fuse is that known as plug fuses. Ordinary plug fuses consist, generally, of an insulating body having two terminals on the outside thereof, so constructed and arranged as to be readily brought in contact with the terminals of an electrical circuit, by way of what is known usually as a fuse block. These fuses are universally used; are made by manydifferent manufacturers; and must all be usable in practically any of the well known forms of fuse blocks; so that they have become, in truth, standard, and may well be referred to as, standard fuse plugs. At any rate they are substantially standard as regards their general external dimensions.

Various forms of plug fuses have been made, especially for the purpose of enabling one to rapidly discern whether or not the fusible or thermal element is intact. It is quite the univer= sal impression that success has not been attained in regard to the feature of indicating the integrity of the fusible element.

A principal object of applicant's invention is to provide a device, which may well be called a combined fuse and fuse integrity indicating device. In providing such a device, applicant has had in mind that it preferably should be in external dimensions substantially the size of the standard 40 plug fuse, so that it may be used with a facility equal to that of a plug fuse in those situations where a plug fuse is now used. A-further object which applicant has in mind in producing his combined fuse and fuse integrity 45 indicator is that the cost must be reduced to a point where, if possible, it approximates the present cost of ordinary plug fuses. .To this end, applicant has, as a further object of his invention, the production of a device in two parts, separable 50 one from the other, one part supporting and protecting the thermal element, which part is removable, and the other part performing the indicating functions desired by applicant, and combinable with the first part to make a complete indicating fuse part.

A further object of applicants invention is to produce a combined fuse and-fuse integrity indicator which will be substantially the same external dimensions as a standard plug fuse.

Other objects and advantages will appear as the description of the particular physical embodiments selected to illustrate the invention progresses, and the novel features will be particularly pointed out in the appended claims.

In describing the invention in detail and the particular physical embodiments selected to illustrate the invention, reference will be had to the accompanying drawing and the several views thereon, in which like characters of reference 7' designate like parts throughout the several views, and in which:

Figure l is a front elevational view of my combined fuse plug and fuse integrity indicator, with the thermal element receiving portion shown separated from. the indicating portion; Fig. 2 is a top plan view of the device as shown by Fig. i; Fig. 3 is a top plan view of the thermal element carrying device as shown by Fig. 1; Fig. 4 is an elevational cross-sectional view on a plane indicated by the line IVIV of Fig. 2 viewed in the so direction of the arrows at the ends of the line; Fig. 5 is an elevational cross-sectional view on the plane indicated by line V--V of Fig. 2 viewed in the direction of the arrows at the ends of the line; Fig. 6 is a cross-sectional view corresponding to that shown by Fig. 4, but illustrated in modified form of contacting means between two elements of the circuit; Fig. 7 is a top plan view of the device as shown by Figs. 4, 5 and 6, but with the top cover plate removed. Applicants device includes generally a thermal element supporting portion T and a thermal element integrity indicating carrying portion I.

The thermal element carrying portion T is in the form, generally, of a hollow cylinder formed with a wall at one end provided with an orifice. This hollow body, designated 1, is formed of in-= sulating material, preferably porcelain, although any one of the many of the common formaldehyde condensation products of phenol may well be used. The hollow body 1 is provided or formed upon its outer periphery with a projection 2 in the form of helix which produces a screw thread for a purpose to be hereinafter more fully described.

Within the interior of the hollow body 1 and preferably formed integrally therewith, is a central pillar 3, provided throughout with a bore 4 which is enlarged at the portion of the pillar adjacent the main body as at 5. 0

A metallic end terminal contact member 6 is inserted in the open end of the enlarged bore 5 651 the body 1, the whole may be screwed into an two portions 6 and 24 will be connected by the so as to project just slightly from the end wall 7 of the hollow body 1. .This terminal contact member is provided with upstanding finger portions 8 and 9 which pass up into the bore and portions thereof then pass through slits 10 and 11. After the portions 8 and 9 are passed through the slits 10 and 11, the terminal portions thereof, 12 and 13, are then turned down sharply at a right angle so as to hold the member 6 securely in place.

At the top of the hollow body 1, a cap 14 is positioned. This cap of conducting material, preferably brass, fits snugly against the outside wall of the body 1, and extends thereover for a short distance so that it is securely held in place. The cap 14 is provided with an opening 15. A disc of transparent material 16, preferably mica, is positioned between the cap and the end wall of the body 1, and is held in position by the cap. The transparent member 16 is orificed at the center thereof to fit a shouldered portion 17 of the central pillar 3.

As the cap 14 forms part of an electrical circuit, and that circuit is made by contact of cap 14 with another portion of the device, to be hereinafter more fully described, applicant forms struck up projections 18 in the upper surface of the cap to facilitate the making of good electrical contact.

A thermal element 19, as best shown in Fig. 4, is attached at one end as by solder 20 to the turned over portion 13 of the terminal contact 6, and the other end is carried across the top or end wall of the body 1, bent over slightly, and then soldered, as at the point 21, to the end cap 14.

The indicator carrying part of applicants device includes a manually manipulative member 22. This member 22 is formed of insulating material, preferably some one of the many formaldehyde condensation products of phenol, although porcelain is quite suitable. Member 22 is formed with a cavity 23. Within the cavity 23 is positioned one end of metallic shell 24. This metallic shell 24 is substantially a hollow cylinder with one end of its wall bent over to form the annular flange 25 designed to rest against the bottom of the cavity 23 while the outer periphery of the shell bears against the side wall of the cavity 23, whereby the shell 24 is held securely in place, although additional fastening means may be employed if found necessary. A large portion of the wall of the shell 24 is formed into helical grooves corresponding and mating with the helical projections 2 upon the thermal element supporting member T so that the shell may be secured in place, as shown in Fig. 4, upon the body 1 so that the flanged portion 25 of shell 24 bears tightly against the projections 18 of the cap 14, thereby making secure and good electrical contact therebetween.

When the member 22 is screwed into place upon ordinary fuse plug. The terminal contact 6 will contact with the ordinary central contact in the ordinary fuse plug, andthe shell 24 will contact with the wall of the ordinary fuse plug. These thermal element 19, so that a fusible member is inserted in circuit, and in order to facilitate this screwing of 22 into place on body 1, and both together into a fuse plug, applicant provides the outer periphery body 22 with corrugations or knurling 26.

Although the portions hereinbefore described combined together, make and are usable as an ordinary plug fuse, and although the portion 22 with the shell 24 may be removed from the body 1 to enable one to peer into the interior of the body 1 through the transparent member 16 in order to ascertain the condition of the thermal element 19, nevertheless, applicant provides a means for determining the integrity of the fusible element 19, without removing any of the device from the thermal element receiving portion.

The indicating means of applicant include a lamp 27. This lamp is preferably of the low voltage discharge type, having two discharge electrodes 28 and 29 therein, provided with the two .usual outside terminals. The lamp is preferably of the neon filled type producing when a discharge between the electrodes occurs, a distinctive color light. The terminals of the lamp are connected, one, 30 to a metallic post 31, fastened in any proper and suitable manner centrally on the body 22, but preferably by molding therein in place. The other terminal 32 of the lamp is connected to one terminal of a resistance 33, the other terminal 34 of which is preferably carried through an orifice 35 in the body 22 and brought out at 36 adjacent the shell 24 and .then soldered thereto. These connections place the lamp 2'? in shunt of the thermal element 19 when the post 31 is connected to terminal member 36. While the thermal element 19 is intact, the lamp 27 does not glow, but upon the destruction or disintegration of the thermal element, the lamp then glows. This is accomplished by means of the resistance 33 which is inserted in series with the lamp 27. This resistance 33 is preferably of the grid leak type and may be of very considerable resistance, say from 50,000 to 100,000 ohms.

In order to connect the post 31 with the terminal contact 6, applicant prefers to provide the terminal contact 6 with contact figures 37 and 38,

so that when themember 22 and the shell 24 is in place upon the body 1 as shown in Fig. 4, metallic post 31 will make good contact between the contact figures 3'7 and 38.

In order to provide a proper receptacle for the lamp 27, applicant prefers to provide a cavity 39 opening in the upper face of the body 22 in which the lamp 27 is positioned. In addition, applicant provides a supplementary cavity 40 opening in the upper face of the body 22 in which the resistance 33 may be placed.

In order to protect the lamp and resistance, applicant prefers to provide a cover plate 41 which is provided with a central observation slip 42 to enable the lamp 2'7 to be seen. The cover plate 41 is preferably held in place upon the body 22 by being provided with two bores, as 43 and 44, for the reception of two rivet members, 45 and 46. The plate 41 is placed with the ends of the rivets extending beyond the face of the covered plate 41 and then the ends of the rivets are headed so as to retain the covered plate in place. Applicant prefers to mold the rivets 45 and 46 in place in the body 22 and prefers to have them. of the hollow form.

In Fig. 6 is shown a modified form of the pillar for making contact with the terminal contact. In this form of pillar, designated 47, a spring pressed plunger 48 forms an extension of the pillar 47 and makes contact with a terminal contact 49 corresponding to contact 6 as shown in Fig. 4.

1,951, soe 3 The plunger 48 fits into a bore of the pillar 47 and between the end of the plunger and the bottom of the bore, is a spring 50 tending toforce the plunger outwardly. The plunger is prevented '5 from separating from the pillar 4'7 by having a pin 51 placed therethrough movable in the slot 52 of the pillar.

Although I have particularly described one particular physical embodiment of my invention and 19 explained the operation, construction and principle thereof, nevertheless, I desire to have it understood that the form selected is merely illustrative, but does not exhaust the possible physical embodiments of the idea of means underlying my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A combined thermal fuse and fuse integrity indicator comprising a thermal element receiving go portion and a separable indicating portion: the thermal element receiving portion including a hollow insulating body provided on its outer surface with a helical projection, and provided with a metallic terminal at one end thereof for oo- 5 operation with a terminal of an electrical circuit .to be protected, and a metallic cap terminal at the other end for cooperation with another terminal of a circuit to be protected; a thermal element connecting the metallic terminal members at each end of the thermal element receiving portion, and positioned in the interior thereof; the separable indicating portion including a metallic portion formed as a helix for cooperation with the helix of a fuse block and for cooperation with the helix formed onthe outer surface'of the thermal element receiving body, and a metallic post for contact with the first mentioned metallic terminal of the thermal element receiving body, and an electric lamp connected between m the last named metallic post and the metallic helix whereby the combined thermal fuse and fuse integrity indicator may be screwed into place in a fuse block thereby inserting the thermal element in series with an electrical circuit, and whereby the lamp will be in shunt of the thermal element and will light when the thermal element is destroyed, and whereby the separable fuse integrity indicator may be combined with another thermal fuse receiving body when the thermal element in one body is destroyed.

2. A combined thermal fuse and fuse integrity indicator comprising two separable portions; a thermal element receiving portion formed of insulating material as substantially a hollow cylinder with one end wall and that end wall formed with an orifice, and the curved outer surface 01 the body formed with a helical projection, means for closing the open end of the body including a metallic cap, a metallic terminal positioned in 0 the orifice in the end wall, and a thermal element connecting the metallic cap and the metallic terminal and positioned within the body; the separable fuse integrity indicator including an insulating body, a metallic shell corrugated to 55 form a helix and formed with a flange at one end supported by the insulating body, said shell mating with the helical projection upon the thermal element receiving body and the flange contacting with the end cap thereof, a metallic post 7 supported centrally of the insulating body and contacting with the end terminal of the body, an electric lamp supported by the insulating body and having terminals, one connected to the metallic post and the other to the metallic shell, and

means for protecting the lamp while allowing it to be visible whereby the metallic shell may be screwed upon the thermal element receiving body with its flange in contact with the metallic cap of the thermal element receiving body and both may be screwed into place in a fuse block whereby the thermal element will be inserted in an electrical circuit and upon the destruction of the thermal element, the lamp will light indicating such destruction.

3. As the thermal element supporting body of a separable combined thermal fuse and fuse, integrity indicator: a substantially cylindrical hollow body of insulating material formed with one end wall and an orifice in said end wall, and the curved surface thereof formed with a-helical projection, a central pillar within the body formed with a bore enlarged at the end adjacent the orifice in the end wall, slits formed between the juncture of the pillar and the end wall of the body, a metallic end terminal provided with right angle finger portions positioned in the orifice of the end wall with the finger portions extending through the slits and bent over so as to hold the terminal in place with its end projecting slightly from the end wall of the body, said terminal further provided that contact fingers extending upwardly into the bore of the pillar and adapted for contact with a metallic post insertable therein, said pillar formed with shoulders at the free end thereof, a centrally apertured disc resting against the shoulders and against the end of the wall of the hollow body, a metallic cap positioned over the disc and bearing against the outside side wall of the hollow body whereby the disc is held in place, and a thermal element connected betwen the terminal contact and the metallic cap.

4. As the thermal element supporting body of a separable combined thermal fuse and fuse integrity indicator: a substantially cylindrical hollow body of insulating material formed with one end wall and an orifice in said end wall, and the curved surface thereof formed with a helical projection, a central pillar within the body formed with a bore enlarged at the end adjacent the ori- 12o fice in the end wall, slits formed between the juncture of the pillar and the end wall of the body, a metallic end terminal provided with right angle finger portions positioned in the orifice of the end wall with the finger portions extending through the slits and bent over so as to hold the terminal in place with its end projecting slightly from the end wall of the body, said pillar formed with shoulders at the free end thereof, a centrally apertured disc resting against the shoulders and against the end of the wall of the hollow body, a metallic cap positioned over the disc and bearing against the outside side wall of the hollow body whereby the disc is held in place, and a thermal element connected between the terminal contact and the metallic cap.

5. As the indicating portion of a combined thermal fuse and fuse integrity indicator: an insulating body formed with a cavity for the reception of one end of a metallic shell and a cavity for 14 the reception of a lamp, a metallic shell cormgated to form an helix having one end flanged and positioned in the cavity of the body whereby it is held securely in place, a metallic post-positioned centrally of the shell and supported by the hollow body adapted to make contact with metallic contact fingers, a lamp positioned in another cavity of the body and having terminals, one connected to the metallic shell, and the other to the metallic post, and a plate formed with an observation slit positioned over the lamp, and means for holding the cover in place.

6. As the thermal element supporting body of a separable combined thermal fuse and fuse integrity indicator: a substantially cylindrical hollow body of insulating material formed on its curved surface with a helical projection forming a screw thread adapted for cooperation with a fuse integrity indicator, a metallic terminal positioned at one end of the hollow body, a metallic cap at the other end of the hollow body, a thermal element connecting the terminal and the cap, and means associated with the metallic terminal adapted to make contact with a conducting member of a fuse integrity indicator.

7. As an indicating portion of a combined thermal fuse and fuse integrity indicator; an insulating body approximating a disc and formed with a cavity in one face for the reception of one end of a metallic shell and in the other face with a cavity for receiving a lamp; a metallic shell corrugated to form a helix having one end flanged and positioned in the cavity in one face of the body and bearing against the side walls thereof whereby the shell is held securely in place; a metallic finger positioned centrally of the shell, supported by the hollow body, and adapted for contact with'a terminal of a thermal element supporting body; a lamp positioned in the other thread adapted to engage a metallic screw threaded shell of a fuse integrity indicator; a metallic terminal positioned on one end of the hollow body adapted to make contact with one side of an electrical circuit to be protected, said metallic terminal including means for making connection to the metallic finger of a fuse in-. tegrity indicator; a hollow guiding collar positioned centrally of the hollow body and adapted to receive and guide the metallic finger of a fuse integrity indicator; a metallic end cap fitted over the end of the hollow body opposite the metallic terminal and adapted to make electrical contact with the metallic screw threaded shell of a fuse integrity indicator; and a thermal element connecting the metallic terminal and the metallic cap.

FRANK C. LA MAR. 

